Fluid pressure responsive device with rupturing diaphragm



1966 cs. L. GLAESER ETAL 3,

FLUID PRESSURE RESPONSIVE DEVICE WITH RUPTURING DIAPHRAGM Filed June 5, 1963 5% ,nfraa.

Pressure E/ecfraless De osited Mefa! INVENTORS. HEM/Ry fidSOL/l k 6 1; 514E555 distended positions of i United States Patent H 3,227,306 FLUID PRESSURERESPONSIVE DEVICE WITH RUPTURING DIAPHRAGM George L. Glaeser and Victor E. Hamren, Los Angeles, and Henry Fascia, Jr., Mar Vista, Califi, assignors to Mechmetal-Tronics, Inc., Culver City, Calif., a corporation of Delaware 3 t Filed June 3, 1963, Sen. No.284,977

13 Claims. ,(Cl. 220-89) This invention relates to fluid. pressure responsive tie- 3,227,305 Patented Jan. 4, 1966 center of diaphragm body 13 is a thinned rupture diaphragm l positioned in. concentric, opposed, axially vices such as bellows and diaphragrns and has as its generalobject to provide an improved terminal pressure responsive device having ,a diaphragm which will rupture at the terminal pressure. The invention is applicable to devices for limiting the pressure inclosed vessels or fluid lines,- acting as a relief device for releasing the fluid pressure in the event a terminal pressure is developed. The invention can also be utilized in other applications, such as in dual fluid container apparatus, for opening a communication port or passage between two initially sepa-rated fiuids so asto permit them to be mixed when 3 a terminal pressureis attained. Other applications "of the invention will suggest themselves tothose skilled in theart. it

The invention providesy a pressure-responsive diaphragm having a thinned rupture area adapted to be distended, bubble-like, under the fluid pressure, in operative association witha stud having a slightly rounded point, supported so as to be substantially unyielding, the

distended diaphragm being pressed against the indenting Stud at terminal fluid pressure and, because it is then stressed under considerable stretch tension, it will rupture when indented to an extent where the stress in the indented area increases beyond the tensile limit of the diaphragm under the opposing forces of fluid pressure distention and indenting. I 5

The invention provides the special advantage that the rupture, once started at the identing area, instantaneously spreads over a relatively large area of the thinned portion of the diaphragm so as to attain instantaneous, substantially full release of pressure. 1 v

Other objects and advantages will become apparent in the ensuing specification and appended drawing in which:

FIG. 1 is an axial sectional view of a pressure responsive device embodying one form of the invention;

FIG. 2 is an end view of the same;

FIG. 3 is a fragmentary axial. sectionalgyiew of the same on a magnified scale, illustrating the retracted and the fluid pressure responsive bellows; p

FIG. 4 is an end view of the bellows of FIG. 1;

FIG. 5 is an end view of .a modified form of the pressure responsive bellows; and

FIG. 6 is a fragmentary view of the device in process of formation. q

Referring now to the drawings in detail, and in particular to FIG. 1, -I have shown the-rein, as an example of one form in which the inventionmay be embodied, a fluid pressure responsive element A mounted on the end of a fitting B which communicates with fluid pressure so designated by the legend in FIG. 1; an indenting stud C disposed in opposed relation to a thinned diaphragm in the center of pressure responsive element A;3and a" spaced relation to an indenting point 16 projecting from the inner end of stud C. In FIGS. 1-4, diaphragm 15 is in the form of a circular disc.

The fitting B may include a tubular neck 17 adapted to. be connected into the wall of a pressurized chamber or fluid line so as to be subjected directly to the fluid pressure in its throat. It may also include a head 18 provided with a coaxial series of passages 18 extending axially therethrough and communicating with the back side of the diaphragm or bellows A. The rim 10 of the bellows is secured and sealed, at 19, in an annular groove 20 in the forward face of the head 18, whereby the fluid pressure is sealed in the throat of fitting 17 and reacts against the bellows A through the passages 18' to distend the bellows as the pressure rises.

The stud C has a shank 25 provided with a thread by which it is mounted in a boss 26 in the supporting cap D, and a suitable head 27 which may have a screwdriver slot 28 for adjusting the position of the stud in its mounting.

It is i-mportant that a sharp piercing point be avoided in thjelindenting point 16, since, if sharp enough, the point. would have a piercing action without sufiicient indenting action to produce the degree of local increase in stress which will trigger the explosive rupture of the rupture disc. The point 16 may have a curved end surface, but one that is of small area. It should be understood that the radius of curvature is greatly exaggerated in the drawing for the purpose of illustrating curvature, and that in fact in some applications, eg in a particular application in which we have used a rupture disc of approximately /2 inch diameter and .0003 inch thickness, we have found that the radius of point 16 can be as low as .0005 inch, and we have selected that radius as an optimum for that particular application. For other applications, the radius may be much greater, so long as the contacting end of the stud Cpresents substantially point contact with the rupture disc.

The mounting cap D functions (1) to mount stud C, and (2) as a guard covering the extremely thin rupture disc 15 and protecting it against accidental damage.

In the particular form shown, it comprises a solid disc against the outer surface of the bellows A.

z The spider 31 abuts a flange 35 on the fitting neck 17 and is secured thereto by cap screws 36. Flangef35 is provided with a circular seal ring 37 seated in a shallow annular face groove 38 on its rear face, whereby the back side of flange 35 may be sealed to the outer wall of a receptacle having a port in which the neck 17 is coupled to the receptacle.

The reentrant bead 14 of the bellows A normally seats against an annular flange 40 on the head 18, flange 40 being separated from the body of head 18 by an annular groove 41 which intersects the outer array of passages 18' and communicates the fluid pressure to the peripheral area'o-f bellows A. T he contact of head 14 against flange 40 supportsthe rupture disc 15 in a position spaced forwardly from the end face of head 18, so that the fluid pressure will be communicated uniformly to the entire rear face of the rupture disc.

The diaphragm body 13 and the remainder of bellows A is much thicker and more rigid than the rupture disc 15, the ratio being such that the diaphragm body A is relatively rigid, although adapted to shift axially in response to fluid pressure (e.g. between the normal unstressed position shown in full lines in FIG. 1 and the distended position shown in broken lines in FIG. 1) so as to bring the rupture disc 15 into contact with the rupture point 16. The rupture disc 15, on the other hand, is much more highly responsive to the fluid pressure than the diaphragm body 13, in a manner such that as the pressure nears the terminal point, the rupture disc 15 will be distended like a bubble, in a stretched condition, with high tretch tension developed therein, approximately as illustrated in the broken line position of FIG. 3.

The diaphragm or bellows is of Mechmetal, a nickel alloy developed by electroless deposit (without use of electricity, and may be fabricated by developing the wall of the diaphragm as a deposited coating upon a pattern or form which is later dissolved out of the completed diaphragm or bellows, as more specifically described in the Patent No. 3,040,426 of Victor Hamren, issued June 26, 1962.

The thinned rupture disc 15 is formed as an initial coating on the form, a fragment of which is indicated at 21 in FIG. 6. This thin coating, indicated at 13 in FIG. 6, will extend uniformly over the surface of the mold as immersed in the nickel alloy solution 22. When the selected thickness for the rupture disc 15 has been attained, the area of the disc is coated with a suitable coating 23 of a barrier material which will protect the surface of disc 15 against contact with the coating solution 22, thus preventing any further build-up of thickness in the disc 15. After the application of the barrier coating 23, the form is placed back in the solution 22 and the remainder of the area is subjected to further deposit of metal until the coating 13' is developed to the selected full thickness for the diaphragm body 13 and the bellows convolutions 11, 12 etc. The form and its deposited coating are then removed from the coating solution, the form is etched out of the bellows, the coating 23 is removed and selected tempering or stress-relieving heat treatment may then be applied to the bellows or diaphragm article to condition the metal to the desired degree of hardness or softness, according to the requirements for the particular article.

The rupture diaphragm 15 may constitute a circular are in the center of the diaphragm as indicated in FIG. 4.

On the other hand it could be a non-circular area of symmetrical form, such as the Maltese cross area 15 of FIG. 5, or could even be of irregular configuration.

As embodied in a bellows of two convolutions as shown in FIG. 3, with the bellows diameter being roughly between /2 inch and one inch and the diameter of the rup ture disc 15 being in the neighborhood of 7 of an inch, the wall thickness of rupture disc 15 may be .0003 inch, whereas the thicker wall of parts 10-13 may be as much as five times as thick (e.g. .00142 inch). For a wall thicknes of .0003 inch, the diameter of rupture disc may vary from a minimum of about inch through an optimum in the range of /2 to inch and up to a diameter of as much as 1 inch or somewhat greater. Where the rupture disc 15 has a wall thickness as great as .001, the diameter of the disc may extend up to a maximum of three or four times as great a the previously stated maximum (e.g. up to 3, 4 or 5 inches).

The ratio of the area of rupture disc 15 to the overall area of the diaphragm or bellows is not as important as the ratio between the area of rupture disc 15 and its thickness. The rupture diaphragm may be of maximum area where it ha the circular form of FIG. 4.

At the terminal pressure for which the unit is designed, the rupture disc 15, under high tensile stress as the result of its ballooning action under the pressure, will make contact with the rupture point 16. As the distension of the disc 15 is continued, the relatively unyielding rupture point 16 will exert highly concentrated axial pressure against a very small area at the center of disc 15, thus greatly magnifying the tensile stress in that small area. At the selected terminal pressure, this magnified tensile stress at the center of the diaphragm will exceed the tensile strength of the diaphragm, causing it to rupture. As soon as a break occurs in the wall of the diaphragm at the central stres point, the diaphragm 15 will be torn apart by the fluid pressing against it, to provide an aperture of sufficient area to release the pressures Thus pressure release i substantially instantaneous.

The spacing between the indenting point 16 and the rupture disc 15 is selected in accordance with the ter-- minal pressure that is established for the unit. Once es tablished, this spacing should remain unchanged at any one temperature. Where the unit is required to operate under conditions involving a fairly wide range of tem-- perature changes, however, the invention provides, a a secondary and improved feature thereof, a compensation for the effect of temperature upon the rupture disc 15. This is accomplished by utilizing the expansion of the mounting cap D away from the fitting B to effect a withdrawal of the stud C away from the rupture disc 15 at a rate substantially matched to the increased distension of the diaphragm at higher temperatures arising from its loss of spring rate with increased temperature. For example, the cap D is molded of a synthetic resin plastic material having a thermal expansion rate which may be as much as ten times the rate of the metal stud C, whereby to elfect such compensating action, the thermal expansion of the stud of considerably shorter axial dimension than the cap D, being negligible.

A special advantage of the invention i its provision for pretesting the unit under over-pressurized conditions.

That is to say, by backing off the indenting stud C, the range of distension of the diaphragm prior to making indenting contact with the stud will be increased, and the stretch-tension developed in the rupture disc of the diaphragm prior to indenting contact will be correspondingly increased beyond the limit at which rupture will occur in the actual operation of the device under its specified conditions. Thus, it is possible to test the rupture disc of the diaphragm for a safety margin in the fluid pressures which will be effectively withstood by the diaphragm in its range of free movement prior to indenting contact with the stud, and thereby the device can be guaranteed to withstand the terminal pressures with no likelihood of being ruptured by fluid pressure alone, without indenting.

I claim:

1. A fluid pressure release device comprising: means providing a throat to be subjected to fluid pressure therein; a pressure-responsive diaphragm closing an end of said throat and movable to a distended position in response to said fluid pressure, said diaphragm having a portion only of uniform thinner thickness than the remainder of said diaphragm and constituting a rupture wall of such area and thinness and flexibility as to undergo distension to a bubble-like condition having high stretch tension such as to cause explosive rupture of said rupture wall in response to application of indenting pressure thereagainst when said diaphragm is in the distended condition; and an indenting stud supported in substantially non-yielding condition opposite said rupture wall normally in axially-spaced relation thereto, in a position in which it will be engaged by said rupture wall when said diaphragm is distended under a selected terminal pressure. in said throat, said indenting stud then applying indent ing pressure to said rupture wall and concentrating said pressure on a small area thereof so as to effect rupture. thereof at said terminal pressure.

2. A fluid pressure release device as defined in claim 1, wherein said diaphragm is of uniform wall thickness except for said rupture wall, which is of uniform thinness less than half the thickness of the remainder of the diaphragm.

3. A fluid pressure release device as defined in claim 2, wherein said rupture wall is of the order of one-fl th the thickness of the remainder of said diaphragm.

4. A fluid pressure release device as defined in claim 1, wherein said rupture wall has a diameter in the range of /z'to 1 inch and a thickness of the order of .0003 inch.

5. A fluid pressure release device as defined in claim 1, wherein said diaphragm is of nickel alloy.

6. A fluid pressure release device as defined in claim 1, including an annular reentrant head in said diaphragm outwardly of and adjacent the periphery of said rupture wall, and means surrounding said throat in fixed relation thereto against which said bead is seated when said diaphragm is not distended. j

7. A'fluid pressure release device as defined in claim 1, including a mounting cap attached to said throat means and mounting said indenting stud, said mounting cap having a high rate of thermal expansion such as to compensate for'the increase in yieldability of said diaphragm resultingfrom temperature rise, so as to maintain a substantially constant rupture response of said diaphragm to theselected terminal pressureQ'at all temperatures.

8. A fluid pressure release device as defined in claim 1, including a mounting cap attached to said throat means and mounting said indenting stud, said mounting cap being of a molded plastic material.

9. fluid pressure release device as defined in claim 1, wherein said diaphragm is embodied in a bellows with a convoluted rim.

10. A fluid pressure release device as definedin claim 1, wherein said diaphragm is embodied in a bellows with a convoluted rim, wherein said rupture wall is of circular disc form, and wherein said diaphragm includes an annular reentrant bead between said bellows and the periphery of said rupture Wall, and means surrounding said throat in fixed relation thereto against which said head is seated when said diaphragm is not distended.

11. A pressure release device as defined in claim 1, wherein said rupture wall is of non-circular form, but symmetrical about the center of said diaphragm.

12. A pressure release device as defined in claim 1, further including a support for said indenting stud, and means for adjusting said stud on said support to vary the axial spacing from said rupture wall.

13. A pressure release device as defined in claim 1, further including a support for said indenting stud, said stud being threaded into said support to provide for adjusting said stud to vary the axial spacing from said rupture wall.

References Cited by the Examiner UNITED STATES PATENTS 766,778 8/1904 Stubbers 22089 1,951,897 3/ 1934 Binckley 22089 2,962,038 11/196'0 Bird 22089 FOREIGN PATENTS 129,460 7/ 1919 Great Britain. 748,953 5/ 1956 Great Britain.

THERON E. CONDON, Primary Examiner. 

1. A FLUID PRESSURE RELEASE DEVICE COMPRISING: MENS PROVIDING A THROAT TO BE SUBJECTED TO FLUID PRESSURE THEREIN; A PRESSURE-RESPONSIVE DIAPHRAGM CLOSING AN END OF SAID THROAT AND MOVABLE TO A DISTENDED POSITION IN RESPONSE TO SAID FLUID PRESSURE, SAID DIAPHRAGM HAVING A PORTION ONLY OF UNIFORM THINNER THICKNESS THAN THE REMAINDER OF SAID DIAPHRAGM AND CONSTITUTING A RUPTURE WALL OF SUCH AREA AND THINNESS AND FLEXIBILITY AS TO UNDERGO DISTENSION TO A BUBBLE-LIKE CONDITION HAVING HIGH STRETCH TENSION SUCH AS TO CAUSE EXPLOSIVE RUPTURE OF SAID RUPTURE WALL IN RESPONSE TO APPLICATION OF INDENTING PRESSURE THEREAGAINST WHEN SAID DIAPHRAGM IS IN THE DISTENDED CONDITION; AND AN INDENTING STUD SUPPORTED IN SUBSTANTIALLY NON-YIELDING CONDITION OPPOSITE SAID RUPTURE WALL NORMALLY IN AXIALLY-SPACED RELATION THERETO, IN A POSITION IN WHICH IT WILL BE ENGAGED BY SAID RUPTURE WALL WHEN SAID DIAPHRAGM IS DISTENDED UNDER A SELECTED TERMINAL PRESSURE IN SAID THROAT, SAID INDENTING STUD THEN APPLYING INDENTING PRESSURE TO SAID RUPTURE WALL AND CONCENTRATING SAID PRESSURE ON A SMALL AREA THEREOF SO AS TO EFFECT RUPTURE THEROF AT SAID TERMINAL PRESSURE. 